Rare earth elements (REE) are generally considered the fifteen lanthanides and scandium and yttrium. Rare earth elements (and compounds that contain them) have many current and potential future uses. Rare earth elements are used as catalysts in the production of glasses and in time-resolved fluorometry and fluorescence resonance energy transfer in drug discovery assays. Current research projects are also investigating the use of some REEs as anticancer agents. Due to their extreme magnetism, certain REEs have also found use in permanent magnets for wind turbines and in motors for hybrid/electric vehicles.
Rare earth elements are not actually rare, but rather fairly plentiful in the Earth's crust. However, REEs are generally dispersed and not typically found in high concentrations like some minerals and ores. They tend to occur together in nature and are generally difficult to separate from one another.